Characterization of Disruption Halo Currents in the National Spherical Torus Experiment
Authors: S.P. Gerhardt, J. Menard, S. Sabbagh and F. Scotti
Abstract:
This paper describes the general characteristics of disruptions halo currents in the
National Spherical Torus Experiment [M. Ono, et al. Nuclear Fusion 40, 557 (2000)].
The commonly observed types of vertical motion and resulting halo current patterns are
described, and it is shown that plasma discharges developing between components can
facilitate halo current flow. The halo current fractions and toroidal peaking factors at
various locations in the device are presented. The maximum product of these two metrics
for localized halo current measurements is always significantly less than the worst-case
expectations from conventional aspect ratio tokamaks (which are typically written in
terms of the total halo current). The halo current fraction and impulse is often largest in
cases with the fastest plasma current quenches and highest quench rates. The effective
duration of the halo current pulse is comparable to or shorter than the plasma current
quench time. The largest halo currents have tended to occur in lower β and lower
elongation plasmas. The sign of the poloidal halo current is reversed when the toroidal
field direction is reversed.
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Submitted to: Nuclear Fusion (November 2011)
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Download PPPL-4755 (pdf 19.62 MB 33 pp)
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